-Single photon emitters (SPEs) are at the basis of many applications for quantum information management. Semiconductor-based SPEs are best suited for practical implementations because of high design flexibility, scalability and integration potential in practical devices. Single photon emission from ordered arrays of InGaN nano-disks embedded in GaN nanowires is reported. Intense and narrow optical emission lines from quantum dot-like recombination centers are observed in the blue-green spectral range. Characterization by electron microscopy, cathodoluminescence and micro-photoluminescence indicate that single photons are emitted from regions of high In concentration in the nano-disks due to alloy composition fluctuations. Single photon emission is determined by photon correlation measurements showing deep antibunching minima in the second order correlation function. The present results are a promising step towards the realization of on-site/on-demand single photon sources in the blue-green spectral range operating in the GHz frequency range at high temperatures.Introduction. -Single photons are ideal "flying" qubits to convey quantum information between distant nodes of a quantum network. Reliable and controlled generation of single photons is therefore a crucial step to develop applications for quantum communication, quantum information processing and quantum metrology [1,2]. Single photons can be emitted in principle by material entities possessing discrete energy levels, as they need a finite time to "recharge" after emission of one photon. The standard method to assess single photon emission is to measure the second order photon correlation function by Hanbury-Brown and Twiss (HBT) interferometry. As shown in Fig. 1, single photons are either reflected or transmitted by a beam splitter, so that the probability of simultaneous detection in the two detectors of the interferometer is zero. The detection events are stored in a Time-Correlated Single Photon Counter (TCSPC), and the resulting correlation function g 2 (τ) shows an

The realization of reliable single photon emitters operating at high temperature and located at predetermined positions still presents a major challenge for the development of solid-state systems for quantum light applications. We demonstrate single-photon emission from two-dimensional ordered arrays of GaN nanowires containing InGaN nanodisks. The structures were fabricated by molecular beam epitaxy on (0001) GaN-on-sapphire templates patterned with nanohole masks prepared by colloidal lithography. Low-temperature cathodoluminescence measurements reveal the spatial distribution of light emitted from a single nanowire heterostructure. The emission originating from the topmost part of the InGaN regions covers the blue-to-green spectral range and shows intense and narrow quantum dot-like photoluminescence lines. These lines exhibit an average linear polarization ratio of 92%. Photon correlation measurements show photon antibunching with a g (2) (0) values well below the 0.5 threshold for single photon emission. The antibunching rate increases linearly with the optical excitation power, extrapolating to the exciton decay rate of ~1 ns -1 at vanishing pump power. This value is comparable with the exciton lifetime measured by time-resolved photoluminescence. Fast and efficient single photon emitters with controlled spatial position and strong linear polarization are an important step towards high-speed on-chip quantum information management.

This work reports an experimental and theoretical insight into phenomena of two-color emission and different electron-hole recombination dynamics in InGaN nanodisks, incorporated into pencil-like GaN nanowires. The studied nanodisks consist of one polar (on c facet) and six (nominally) identical semipolar (on r facets) sections, as confirmed by transmission electron microscopy. The combination of cathodoluminescence with scanning electron microscopy spatially resolves the nanodisk two-color emission, the low-energy emission (∼500 nm) originating from the polar section, and the high-energy emission (∼400 nm) originating from the semipolar section. This result has been directly linked to a "facet-dependent" nanodisk composition, the In content being significantly higher in the polar (∼20%) vs semipolar (∼10%) section (as quantified by energy dispersive x-ray spectroscopy), further leading to a strong facet-dependent strain anisotropy. Time-resolved cathodoluminescence reveals significantly different electron-hole recombination times in the two sections, moderately fast (∼1.3 ns) vs fast (∼0.5 ns) in polar/semipolar sections, respectively, the difference being linked to a strong anisotropy in the nanodisk internal electric fields. To determine the influence of each of the three contributing "facet-related" anisotropies (composition, strain, and electric field) on the two-color emission, a proper simulation [relying on virtual crystal approximation and involving three-dimensional (3D) continuum mechanical modeling, a 3D Poisson equation, and a one-dimensional Schrödinger equation] has been performed. The theoretical simulations allow the three effects to be quantitatively disentangled, revealing a clear hierarchy among their contributing weights, the facet-dependent composition inhomogeneity being identified as the dominant one (and the strain inhomogeneity being identified as the least significant one). As for different recombination times, while it is mainly linked to the internal electric field anisotropy, we also suggest that it is, very likely, influenced by gradually increasing In content along the nanodisk growth direction (lattice-pulling effect); the latter mechanism keeps electrons and holes in (relative) proximity within the polar section, enabling their relatively fast and efficient radiative recombination.

We present a detailed examination of a multiple InxGa1-xN quantum well (QW) structure for optoelectronic applications. The characterization is carried out using scanning transmission electron microscopy (STEM), combining high-angle annular dark field (HAADF) imaging and electron energy loss spectroscopy (EELS). Fluctuations in the QW thickness and composition are observed in atomic resolution images. The impact of these small changes on the electronic properties of the semiconductor material is measured through spatially localized low-loss EELS, obtaining band gap and plasmon energy values. Because of the small size of the InGaN QW layers additional effects hinder the analysis. Hence, additional parameters were explored, which can be assessed using the same EELS data and give further information. For instance, plasmon width was studied using a model-based fit approach to the plasmon peak; observing a broadening of this peak can be related to the chemical and structural inhomogeneity in the InGaN QW layers. Additionally, Kramers-Kronig analysis (KKA) was used to calculate the complex dielectric function (CDF) from the EELS spectrum images (SIs). After this analysis, the electron effective mass and the sample absolute thickness were obtained, and an alternative method for the assessment of plasmon energy was demonstrated. Also after KKA, the normalization of the energy-loss spectrum allows us to analyze the Ga 3d transition, which provides additional chemical information at great spatial resolution. Each one of these methods is presented in this work together with a critical discussion of their advantages and drawbacks.

Self‐assembled nanocolumns (NCs) with InGaN/GaN disks constitute an alternative to conventional light emitting diodes (LED) planar devices [1]. However, their efficiency and reliability are hindered by a strong dispersion of electrical characteristics among individual nanoLED. Polychromatic emission derives from an inhomogeneous distribution of indium concentration due to the inherent tendency of InGaN alloys to develop composition fluctuations as a function of the polarity of the growth crystallographic planes [2]. The recent development of selective area growth of NCs by molecular beam epitaxy has allowed the achieving of highly homogeneous and controllable GaN/InGaN NCs with improved crystalline quality and higher control over the indium distribution [3]. In this work, we present the characterization performed on LEDs based on ordered NCs with InGaN active disks (figure 1). The detailed structural characterization of the nanostructures has been performed by scanning transmission electron microscopy (STEM) carried out on an aberration‐corrected JEOL‐JEMARM200 microscope. High crystal quality of the NCs is set by the analysis of atomically‐resolved high angle annular dark field (HAADF) images. The indium distribution within the InGaN disks is studied by EDS elemental mapping while the polarity of the semiconductor NCs is followed by locating the nitrogen atomic columns in annular bright field (ABF) images while (figure2). Direct correlation of the optical and structural properties on a nanometer‐scale was achieved using low temperature cathodoluminescence (CL) spectroscopy in an FEI STEM Tecnai F20 [4].